The invention relates to an anti-adhesion coating for welding and soldering devices as well as electric contacts and to a process for manufacturing same. A preferred field of application is the protection of holding, guiding and fixing devices of welding and/or soldering devices, particularly of automated welding lines in automobile construction.
U.S. Pat. No. 4,156,807 suggests applying a boron nitride layer for protecting a workpiece from metallic contaminations in the form of hot welding spatters or welding beads. Boron nitride is very resistant to temperature changes and therefore prevents thermally caused damage to the workpiece by hot metallic contamination. However, boron nitride is relatively soft, so that, depending on the application condition of the workpiece to be machined, the layer may suffer mechanical damage and the protective effect may therefore be lost. Furthermore, boron nitride is a good electric insulator whose insulation characteristic is undesirable, for example, when electric contacts are to be protected. Another considerable disadvantage is the only moderate anti-adhesion effect of boron nitride with respect to metallic contaminations.
German Patent Document DE 41 10 539 A1 teaches the protection of a highly copper-containing component against microscopic or macroscopic contaminations, such as flue gases or splatters of liquid metal, by a protective layer of titanium nitride or titanium carbonitride. Because the electrical properties of the components of German Patent document DE 41 10 539 A1 are to be changed as little as possible, these titanium-based hard materials are very suitable because of their high temperature stability and their good electrical conductivity. As in the case of boron nitride, their only moderate anti-adhesion effect with respect to metallic contaminations is disadvantageous. Furthermore, they have the disadvantage that these protective layers can be deposited during PVD and CVD process at typically relatively high temperatures of more than 450xc2x0 C. Such protective layers on a titanium basis can therefore not be used or can be used only to a limited degree in the case temperature-susceptible substrates. Furthermore, the good electrical conductivity of the anti-adhesion coating may be undesirable depending on the application.
When protecting surfaces against metallic contamination, such as contaminations of welding processes, as in the above-mentioned patent documents, in addition to the thermal protection of the surface, it is also important that the metallic contaminations do not adhere to the surface. Adhering metallic contaminations may result in mechanical as well electric malfunctioning.
For welding and hard soldering purposes, guiding, fixing and clamping devices made of steel and materials for casting are frequently used which, with respect to metallic contaminations, because of similarly high values in the total surface energy "sgr"tot, have a strong tendency to adhere. Adhering metallic contaminations result in an inaccuracy of measurements of the above-mentioned devices, which therefore must be frequently exchanged or reworked. Such problems occur, for example, in automated welding lines, for example, in automobile construction or during the manufacturing of pipes.
In addition, there are electrical components, such as tips of contacts, contact springs or contact terminals, which are provided in the electrical industry for testing the performance of electronic components and which frequently come in contact with soft solders. Because of the low solder temperatures of initially maximally 450xc2x0 C., the providing of a thermally stable protection layer is therefore not as required as the providing of a protective layer which prevents the adhering of the spread-on soft, usually tin or lead-containing solder. However, adhering metallic solder uncontrollably affects the electric contact, which results in electrical malfunctioning. Such contacts frequently consist of nonferrous metal alloys and, for the above-mentioned reasons, are often protected by galvanic layers with Cr, Ni, Ag, Au. Although these layers have the required electrical conductivity, they are quite soft and are rapidly abraded.
It is an object of the invention to largely avoid the problems of the prior art and to provide an alternative for the above-mentioned protective layers against metallic contaminations from welding and soldering processes. This alternative protective layer is to be thermally stable and is to have particularly good anti-adhesion characteristics with respect to the usually ductile metallic contaminations. The anti-adhesion effect is to exist particularly with respect to the normally used materials of the welding and soldering systems, that is, predominantly with respect to steel and diecast material.
Another object consists of providing a hard protective layer with good wear and friction properties in order to be mechanically usable in a manner which is as universal as possible.
Another object is the providing of an anti-adhesion layer which can be varied in its electrical conductivity so that it can be used as universally as possible with respect to its electrical behavior.
Another object consists of providing an anti-adhesion layer against metallic contaminations which, when it is applied to the workpiece or component to be protected, if possible, does not damage the workpiece or component.
According to the invention, these objects can be achieved by an anti-adhesion coating according to the present invention. Advantageous further developments of the anti-adhesion coating according to the invention are indicated in the dependent claims. The process for manufacturing these coatings takes place according to the present invention.